Dobsonfly
Dobsonflies are a subfamily of insects, Corydalinae, part of the Megalopteran family Corydalidae. The larvae (commonly called hellgrammites) are aquatic, living in streams, and the adults are often found along streams as well. The nine genera of dobsonflies are distributed throughout the Americas, Asia, and South Africa. Description Adult dobsonflies are some of the largest non-Lepidopteran insects of temperate zones such as the United States and Canada, with a wingspan of up to 180 mm in some species of Corydalus.1 A species in China has been reported with a wingspan of 21 cm.2 The wings vary from a grayish to translucent shade, depending on the species, and the anal region of the hindwing is wide and folded at rest. Despite the large wings, adults are weak, fluttery fliers. The body is soft and reaches up to 75 mm in length, and coloration varies from yellow to dark shades of brown.1 Male adults are easily recognized by their long, curving mandibles, reaching up to 40 mm in length, which they use in competition for females.3 It is possible that the mandibles may have been selected as secondary sex characteristics used by females to evaluate males during courtship. Males cannot use these mandibles to bite because they are too long; on the other hand, females have short, heavily sclerotized mandibles which enable them to deliver powerful bites when threatened.1 The antennae of males are also noticeably elongated, even longer than the mandibles. Corydalinae is distinguished from closely related clades by the following synapomorphies (with exceptions in a few species): quadrate head with a postocular spine, ridge, and plane, non-pectinate antennae, four crossveins between the radius and the radial sector, and distinctive male terminalia with a well developed ninth gonostylus.1 In regards to the larvae, entomologist John Henry Comstock wrote in his 1897 book Insect Life,4 "In spite of its disagreeable appearance it is in some respects very interesting to students of Nature study." The larvae, commonly called hellgrammites, are perhaps better known than the adults due to their more readily findable nature. They are unusual in that although they are generally aquatic, taking in dissolved oxygen through abdominal lateral filaments and tracheal gills, they also have spiracles that allow them to take in air directly when above water.5 Larvae of dobsonflies differ from those of their sister clade, the alderflies, in that they bear eight pairs of lateral processes as well as anal prolegs with a pair of terminal hooks used to hold themselves to substrate, and also in that they lack a terminal filament.6 At the end of the abdomen is a pair of claw-like structures. Body color is black or dark brown. Diet and Behavior The larvae of dobsonflies live along the rocky bottoms of streams. Chiefly active during the night, they ambush prey in the middle of riffles which supply plenty of oxygen and stir up prey.7 They are generalist predators; dissections have revealed that they primarily eat aquatic immatures of mayflies, caddisflies, stoneflies, and chironomid midges.8 Although the larvae spend most of their lives under rocks below water, locals along Virginia rivers have reported emergences, known as "hellgrammite crawlings," during thunderstorms.9 The adults are also nocturnal, and are seldom seen as they hide under leaves in the canopy during the daytime. However, they do sometimes form aggregations under bridges or other structures along streams.5 Since the adults live only about a week, they are not known to eat anything, although they have been reported to drink sweet solution in captivity.5 The dobsonfly may be attracted by mercaptan, an indicator additive in natural gas and propane, and may behave as an animal sentinel in the presence of these gasses. Life cycle Category:Corydalidae